JP6656718B2 - Negative electrode including multiple protective layers and lithium secondary battery including the same - Google Patents

Description

  This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0120602 filed on Sep. 21, 2016 and Korean Patent Application No. 10-2017-0092180 filed on Jul. 20, 2017. All contents disclosed in the application documents are included as part of the present specification.

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode including a multi-layered protective layer and a lithium secondary battery including the same. And a lithium secondary battery including the same.

  Recently, interest in energy storage technology has been increasing. The field of application has expanded to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, and efforts to research and develop electrochemical devices have been increasingly embodied.

  Electrochemical devices are the area that has received the most attention in this regard, and the development of rechargeable and rechargeable batteries has been the focus of attention, and recently, in developing such batteries, Research and development on new electrode and battery designs to improve capacity density and energy efficiency are being pursued.

  Among the currently used secondary batteries, lithium secondary batteries developed in the early 1990's have been replaced with conventional batteries such as Ni-MH, Ni-Cd, and sulfate-lead batteries using an aqueous electrolyte solution. Compared with the advantages of a higher operating voltage and a much higher energy density, they have been spotlighted.

  The lithium secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separation membrane interposed between the positive electrode and the negative electrode is stacked or wound, and the electrode assembly is built in a battery case. , And a non-aqueous electrolyte is injected therein. The lithium secondary battery generates electric energy by an oxidation and reduction reaction when lithium ions are inserted / desorbed between a positive electrode and a negative electrode.

  In general, a negative electrode of a lithium secondary battery uses lithium metal, carbon, or the like as an active material, and a positive electrode uses lithium oxide, a transition metal oxide, a metal chalcogen compound, a conductive polymer, or the like as an active material.

  Among them, a lithium secondary battery using lithium metal as a negative electrode generally attaches a lithium foil on a copper current collector or uses a lithium metal sheet itself as an electrode. Lithium metal has attracted great interest as a high-capacity negative electrode material because of its low potential and large capacity.

  When lithium metal is used as the negative electrode, unevenness in electron density may occur on the surface of the lithium metal due to various factors when the battery is driven. Here, lithium dendrites in the form of tree branches are generated on the electrode surface, and protrusions are formed or grow on the electrode surface, so that the electrode surface is very rough. Such lithium dendrite may cause deterioration of the battery performance and, in severe cases, damage to the separator and short circuit of the battery. As a result, the temperature inside the battery rises, and there is a risk of explosion and fire of the battery.

  In order to solve this problem, studies have been made to incorporate a polymer protective layer or an inorganic solid protective layer into the lithium metal layer, increase the salt concentration of the electrolyte, and apply an appropriate additive. However, the effect of such research on suppressing lithium dendrite is only a slight fact. Therefore, solving the problem through deformation of the lithium metal negative electrode itself is an effective alternative.

Korean Registered Patent Publication No. 10-162410 "Lithium Electrode and Lithium Secondary Battery Containing It" Korean Patent Application Publication No. 10-2016-0052351 "Lithium metal electrode having stable protective layer and lithium secondary battery including the same"

  As described above, the lithium dendrite of the lithium secondary battery is deposited on the surface of the negative electrode, which may cause volume expansion of the cell. Here, as a result of various studies, the inventor of the present invention has found a method that can solve such a problem caused by dendrite by modifying the structure of the electrode, and has completed the present invention.

  Therefore, an object of the present invention is to provide a lithium secondary battery having improved battery performance by solving the problem of cell volume expansion due to lithium dendrite by deforming the electrode structure.

To achieve the above objectives,
The present invention relates to a lithium metal layer;
A first protective layer formed on the lithium metal layer and maintaining an interface with the lithium metal layer;
A second protective layer formed on the first protective layer and physically suppressing dendrite growth; and a third protective layer formed on the second protective layer and supporting a structure of the second protective layer; The present invention provides a negative electrode for a lithium secondary battery, comprising:

At this time, the first protective layer may have an ionic conductivity of 10 ⁻⁷ S / Cm or more and an electrolyte absorbency of 150 wt% or more.

  In this case, the first protective layer may include at least one selected from the group consisting of PVDF-HFP (poly (vinylidene fluoride-co-hexafluoropropylene)) polymer, polyurethane-based polymer and polyacryl-based polymer. Can be.

At this time, the second protective layer has a Young's modulus of 5 GPa or more, a Li ion conductivity of 10 ⁻⁷ S / Cm or more, and an electrolyte absorbency of 150 wt% or less. Is also good.

In this case, the second protective layer, LiPON (Lithium Phosphorus Oxynitride), LiBON (Lithium Boron Oxynitride), zirconium oxide, beta-alumina, LISICON (Lithium Super Ionic Conductor) _{compound, Li 2 S-P 2 S} 5 based _{compound, Li 3 N, LiI, Li} 5 NI 2, Li 3 N-LiI-LiOH, LiSiO 4, LiSiO 4 -LiI-LiOH, Li 2 SiS 3, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, _{Li 2 S, Li 2 S-} SiS 2, Li 2 S-GeS 2, Li 2 S-B 2 S 5, Li 2 S-Al 2 S 2, Li 2 O-Al 2 O 3 -TiO 2 -P 2 O ₅ (LATP), CaF ₂ , AgI, RbAg ₄ I ₅ , PVdF-HFP polymer, polyurethane-based polymer, polypropylene-based polymer, and polycarbonate-based polymer.

At this time, the third protective layer may have an ionic conductivity of 10 ⁻⁵ S / Cm or more and an electrolyte absorption of 150 wt% or less.

  In this case, the third protective layer may include at least one selected from the group consisting of a PVdF-HFP polymer, a polyurethane polymer, and a polyacryl polymer.

The present invention also provides a lithium secondary battery comprising: a lithium metal layer; and three or more layers independently selected from the group consisting of a dendrite growth suppressing layer, a single ion conductive layer, and a polymer layer. Provided is a negative electrode for a battery.

  At this time, the dendrite growth suppressing layer may include at least one selected from the group consisting of PVdF-HFP polymer, LiPON, LiBON, polyurethane-based polymer, polypropylene-based polymer, and polycarbonate-based polymer.

  The present invention also provides a lithium secondary battery including the negative electrode.

  The multiple protective layer according to the present invention can physically suppress the growth of lithium dendrite on the surface of the electrode, effectively transmit lithium ions to the lithium metal electrode, and have excellent ion conductivity to protect the metal. Since the layer itself does not act as a resistance layer and an overvoltage is not applied at the time of charge / discharge, the performance of the battery can be prevented from deteriorating, and stability can be ensured when the battery is driven.

  Therefore, the lithium electrode including the multiple protective layer presented in the present invention can be preferably applied as a negative electrode of a lithium secondary battery, which can be used for various devices, for example, most small electronic devices using lithium metal as a negative electrode. It is applicable to a large-capacity energy storage device and the like.

1 is a schematic view of an electrode for a lithium secondary battery according to an embodiment of the present invention.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art to which the present invention belongs can be easily implemented. However, the present invention may be embodied in several different forms and is not limited to this description.

The present invention relates to a lithium metal layer 110;
A first protective layer 120 formed on the lithium metal layer 110 to maintain an interface with the lithium metal layer 110;
A second protective layer 130 formed on the first protective layer 120 and physically suppressing dendrite growth; and a second protective layer 130 formed on the second protective layer 130 and supporting the structure of the second protective layer 130. And a negative electrode 100 for a lithium secondary battery, comprising: a third protective layer 140;

  FIG. 1 is a view illustrating a negative electrode 100 for a lithium secondary battery according to an embodiment of the present invention.

  Referring to FIG. 1, a first protective layer 120, a second protective layer 130, and a third protective layer 140 are sequentially formed on a lithium metal layer 110 in a negative electrode 100 for a lithium secondary battery of the present invention. In this drawing, the first protective layer 120, the second protective layer 130, and the third protective layer 140 are formed only on one surface of the lithium metal layer 110, but may be formed on both surfaces.

  Generally, when lithium metal is used as a battery negative electrode, the following problems exist. First, lithium is an alkali metal and reacts explosively with water, making it difficult to produce and use in a general environment. Second, when lithium is used as the negative electrode, it reacts with the electrolyte, water, impurities in the battery, lithium salts, etc. to form a passivation layer. Form lithium dendrites in the shape of In addition, the dendrite thus formed may grow and cause a direct internal short circuit with the positive electrode beyond the space between the separators, thereby causing a battery explosion. Third, since lithium is a soft metal and has low mechanical strength, it is very difficult to handle without further surface treatment.

  Here, in the present invention, the formation of the first protective layer 120, the second protective layer 130, and the third protective layer 140 on the lithium metal layer 110 can prevent dendrite growth.

  According to an embodiment of the present invention, the lithium metal layer 110 may use a plate-shaped metal. The width of the lithium metal layer 110 can be adjusted according to the shape of the electrode so that the electrode can be easily manufactured. The thickness of the lithium metal layer may be 1 to 50 μm.

Since the first protective layer 120, the second protective layer 130, and the third protective layer 140 are stacked on the lithium metal layer 110, smooth movement of lithium ions between the lithium metal layer 110 and the electrolyte is achieved. Therefore, ion conductivity for lithium ions is basically required. Therefore, it is preferable that all of the three protective layers have Li ion conductivity of at least 10 ⁻⁷ S / Cm or more.

  In addition, the first protective layer 120, the second protective layer 130, and the third protective layer 140 have the respective roles described below in the triple-layered structure. The effect of suppressing the growth of GaN and the effect of maintaining the ionic conductivity are the best.

  In addition, the protective layer may require an electrolyte absorbency (uptake) of a certain range or more or less, but the first protective layer may have an electrolyte absorbency of 150% or more, The protective layer and the third protective layer may have an electrolyte absorbency of 150% or less.

  Here, the electrolytic solution absorbance means how the protective layer can absorb the electrolytic solution, and how much the mass after absorption of the protective layer increases compared to the mass before absorbing the electrolytic solution. To show. The first protective layer may have an electrolyte absorbency of 150% or more and may have a high ionic conductivity. The first protective layer is physically flexible and can wrap the growing lithium. The interface between the second protective layers can be maintained. Since the second protective layer and the third protective layer have an electrolyte absorbency of 150% or less, they have relatively hard physical properties, and can effectively suppress dendrite formation.

  According to an embodiment of the present invention, the first protective layer 120 is formed on the lithium metal layer 110 and an interface between the lithium metal layer 110 and the protective layer during charging and discharging of the lithium ion battery. To maintain the role.

The first protective layer 120 may have a Li ion conductivity of 10 ⁻⁷ S / Cm or more and an electrolyte absorbency of 150% by weight or more, preferably 150 to 250% by weight. , A PVdF-HFP polymer, a polyurethane polymer, and a polyacrylic polymer. The first protective layer 120 is suitable for maintaining an interface because it is physically relatively flexible due to high electrolyte absorption.

In the PVdF-HFP, the content of HFP may be 15% by weight or more, the shore hardness of the polyurethane polymer may be 80A or less, and the crosslink density of the polyacrylic polymer. ^{May be} 10 ⁻⁴ mol / g or less. If the Shore hardness is too low, the impregnation amount of the electrolytic solution becomes too large, and the volume of the battery may increase.If the crosslink density is too high, the ionic conductivity decreases and the resistance increases. There is.

  When the first protective layer 120 is not formed, the interface between the lithium metal layer 110 and the protective layer is not maintained in the lithium ion battery, so that the battery capacity may decrease due to an increase in resistance.

  Accordingly, it is sufficient that the first protective layer 120 is applied only enough to maintain the interface, and if the first protective layer 120 is too thick, the thickness of the electrode is unnecessarily increased. Layer 120 may have a thickness of 1-10 μm.

  According to an embodiment of the present invention, the second protective layer 130 is formed on the first protective layer 120 and serves to physically suppress dendrite growth.

Accordingly, the second protective layer 130 preferably has high physical strength and ionic conductivity. The second protective layer 130 may have a Young's modulus of 5 GPa or more, a Li ion conductivity of 10 ⁻⁷ S / Cm or more, and an electrolyte absorption of 150 wt% or less. Preferably, it may be 30 to 150% by weight.

The second protective layer 130, LiPON, LiBON, zirconium oxide, beta-alumina, LISICON (Lithium Super Ionic Conductor) _{compound, Li 2 S-P 2 S} 5 based _{compounds, Li 3 N, LiI, Li} 5 _{NI 2, Li 3 N-LiI} -LiOH, LiSiO 4, LiSiO 4 -LiI-LiOH, Li 2 SiS 3, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, Li 2 S, Li 2 S-SiS 2 _{, Li 2 S-GeS 2,} Li 2 S-B 2 S 5, Li 2 S-Al 2 S 2, Li 2 O-Al 2 O 3 -TiO 2 -P 2 O 5 (LATP), CaF 2, AgI _{, RbAg 4 I 5, PVdF-} HFP polymer, polyurethane polymer, polypropylene-based polymer and It can include one or more selected from the group consisting of polycarbonate-based polymer.

  In the PVdF-HFP, the HFP content may be 5% by weight or less, the polyurethane polymer may have a Shore hardness of 75D or more, and the porosity of the polypropylene polymer may be 5 to 50%. %. When the Shore hardness is less than the above range, it may be difficult to physically suppress dendrite growth. If the porosity is too low, the capacity may decrease due to an increase in the resistance. If the porosity is too high, it may be difficult to suppress dendrite growth.

  The Young's modulus is a modulus of elasticity that indicates a degree of elongation and a degree of deformation of the object when the object is stretched in both directions, and is also referred to as a length elastic modulus. The second protective layer 130 physically grows dendrite. To suppress this, it is preferable to have a Young's modulus of a certain range or more in physical properties. Methods for measuring Young's modulus are known to those skilled in the art, and one exemplary instrument used to measure Young's modulus is a Universal Testing Machine.

  The second protective layer 130 not only suppresses the growth of dendrite but also has conductivity, so that lithium ions can be smoothly transmitted to the electrodes, thereby extending the life of the battery and improving the performance of the battery. .

  In addition, if the thickness of the second protective layer 130 is too small, it may be difficult to effectively suppress the growth of dendrite. On the other hand, if the thickness is too large, the relative capacity may be increased due to an unnecessary increase in thickness. Since the loss may occur, the thickness of the second protective layer 130 may be 1 to 10 μm.

  According to an embodiment of the present invention, the third protective layer 140 is formed on the second protective layer 130 and serves as a support for supporting the structure of the second protective layer 130. That is, the third protective layer 140 physically supports the second protective layer 130.

The third protective layer 140 may have an ionic conductivity of 10 ⁻⁵ S / Cm or more and an electrolyte absorbency of 150 wt% or less, preferably 10 to 150 wt%. It may include at least one selected from the group consisting of a PVdF-HFP polymer, a polyurethane-based polymer, and a polyacryl-based polymer.

The PVdF-HFP may have an HFP content of 5 to 15% by weight, the polyurethane polymer may have a Shore hardness of 80A to 75D, and the polyacrylic polymer has a crosslink density of 0%. 0.01 M / cm ³ or more.

  Also, if the thickness of the third protective layer 140 is too small, it may be difficult to support the structure of the second protective layer 130. On the other hand, if the thickness is too large, the relative thickness may be increased due to an unnecessary increase in thickness. Since a loss may occur, the thickness of the third protective layer 140 may be 1 to 10 μm.

An electrolyte salt such as a lithium salt may be added to the polymer included in the first protective layer, the second protective layer, and the third protective layer in order to improve Li ion conductivity. What is usually used as an electrolyte for a lithium secondary battery may be used without limitation. For example, as the anion of the lithium salt, F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , NO ₃ ⁻ , N (CN) ₂ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , (CF ₃ ) ₂ PF ₄ ⁻ , (CF ₃ ) ₃ PF ₃ ⁻ , (CF ₃ ) ₄ PF ₂ ⁻ , (CF ₃ ) ₅ PF ⁻ , (CF ₃ ) ₆ P ⁻ , CF ₃ SO ₃ ⁻ , CF ₃ CF ₂ SO _{^{3 -, (CF 3 SO 2}} ) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C - ^{_{, (CF 3 SO 2) 3}} C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - consists ^- and _{(CF 3 CF 2 SO 2)} 2 N It can include one or more selected from the group.

  The method of forming the first protective layer 120, the second protective layer 130, and the third protective layer 140 is not particularly limited, and when the PVdF-HFP polymer, the polyurethane-based, the polyacryl-based, or the polypropylene-based polymer is used, After the polymer or monomer is mixed with the solvent coating solution, it can be formed by using reactive sputtering, microgravure coating, comma coating, slot die coating, spray coating, dip coating, flow coating, etc. Not done. In addition, the solid electrolyte such as LiPON and LiBON can be used by mixing with a binder or the like in a powder state.

  According to a preferred embodiment of the present invention, the negative electrode for a rechargeable lithium battery includes a first protective layer containing 20% by weight of HFP PVdF-HFP, a second protective layer containing LiPON and 5% by weight of HFP on a lithium metal layer. % Of PVdF-HFP, and may be manufactured by laminating a third protective layer. The lithium electrode having such a structure can effectively suppress dendrite growth.

  The electrode for a lithium secondary battery according to the present invention may have various widths and lengths depending on a form processed into a battery. If necessary, the electrodes for lithium secondary batteries manufactured in various widths can be wound and cut when necessary.

The present invention also provides a lithium secondary battery comprising: a lithium metal layer; and three or more layers independently selected from the group consisting of a dendrite growth suppressing layer, a single ion conductive layer, and a polymer layer. A negative electrode for a secondary battery is provided.

  The dendrite growth suppressing layer means the second protective layer 130, and may include at least one selected from the group consisting of LiPON, LiBON, polyurethane-based polymer, polypropylene-based polymer, and polycarbonate-based polymer. .

  The single ion conductive layer may include inorganic, organic, and mixed organic-inorganic polymeric materials. The term "single ion conducting layer" as used herein means a layer that selectively or exclusively allows the passage of a single load of cations. The single ion conducting layer has the ability to selectively or exclusively transfer cations, such as lithium ions, and includes, for example, the polymers disclosed in US Pat. No. 5,731,104 (Ventura, etc.). be able to. In one embodiment, the single ion conductive layer can include a single ion conductive glass that is conductive for lithium ions. Some suitable glasses can be characterized as including "modifier" and "network" moieties known in the art. The modifier may be a metal oxide of a conductive metal ion, typically in glass. The network former may typically be a metal chalcogenide, for example, a metal oxide or sulfide.

  Further, the single ion conductive layer is formed of lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium phosphorous oxynitride, lithium silicosulfide, lithium germanosulfide, lithium lanthanum oxide, lithium titanium oxide, lithium borosulfide. And a vitreous layer containing a vitreous material containing at least one selected from the group consisting of lithium aluminosulfide and lithium phosphosulfide. In one embodiment, the single ion conducting layer can include lithium phosphorous oxynitride. Lithium phosphorous oxynitride electrolyte films are disclosed, for example, in U.S. Patent No. 5,569,520 (Bates).

  The polymer layer may include, but is not limited to, one or more selected from the group consisting of an electrically conductive polymer, an ion conductive polymer, a sulfonated polymer, and a hydrocarbon polymer. Suitable electrically conductive polymers include, but are not limited to, poly (p-phenylene), polyacentylene, poly (phenylene vinylene), polyazulene, poly (ferinaphthalene), polyacene and poly (naphthalene-2,6-diyl). And those described in US Patent No. 5,648,187 (Skotheim). Suitable ionic conductive polymers can also include ionic conductive polymers known as being useful as solid and gel polymer electrolytes for lithium electrochemical cells, such as polyethylene oxide. Suitable sulfonated polymers can include sulfonated siloxane polymers, sulfonated polystyrene-ethylene-butylene polymers, and sulfonated polystyrene polymers. Also, suitable hydrocarbon polymers can include ethylene-propylene polymers, polystyrene polymers, and the like.

  Also, the polymer layer can be used as a protective coating layer for alkyl acrylates, glycol acrylates, polyglycol acrylates, polyglycol vinyl ethers, polyglycol divinyl ethers and separator layers in US patent application Ser. No. 09 / 399,967 (joint application). Cross-linked polymeric materials formed from the polymerization of monomers including those described in Ying et al. For example, the crosslinked polymeric material may be polydivinyl poly (ethylene glycol). The crosslinked polymeric material may further include a salt, for example, a lithium salt, to enhance ionic conductivity. In one embodiment, the multi-layer polymer layer may include a cross-linked polymer.

  However, effective dendrite growth suppression may be difficult in the respective layers, the dendrite growth suppression layer physically suppresses the growth, and the single ion conductive layer and the polymer layer support the suppression layer. And an effect of assisting stable suppression can be obtained. Therefore, when the respective layers are laminated in a composite manner, the effect of suppressing dendrite growth may be improved.

  In addition, the present invention provides a lithium secondary battery including the negative electrode 100.

  The structure of the lithium secondary battery according to the present invention, except for the structure and characteristics of the negative electrode 100, can be manufactured through a known technique performed by a general engineer, and will be described in detail below.

  A general lithium secondary battery includes a negative electrode; a positive electrode; a separator interposed therebetween; and an electrolyte. The negative electrode of the lithium secondary battery of the present invention includes the negative electrode including the multiple protective layer of the present invention. May be included.

  The positive electrode may be manufactured in the form of a positive electrode by forming a composition including a positive electrode active material, a conductive material, and a binder on a positive electrode current collector.

The positive active _{material, LiCoO 2, LiNiO 2, LiMnO} 2, LiMn 2 O 4, Li (Ni a Co b Mn c) O 2 (0 <a <1,0 <b <1,0 <c <1, _{a + b + c = 1)} , LiNi 1-y coyO 2, LiCo 1-y MnyO 2, LiNi 1-y MnyO 2 (O ≦ y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2 , 0 <b <2, 0 <c <2, a + b + c = 2), LiMn ₂ -zNizO ₄ , LiMn ₂ -zCozO ₄ (0 <z <2), LiCoPO ₄ and LiFePO ₄ Any one of them, or a mixture of two or more thereof can be used. Further, in addition to such an oxide, a sulfide, a selenide, a halide, and the like can be used. In a more preferred example, the positive electrode active material may be LiCoO ₂ suitable for a high-power battery.

  The conductive material is a component for further improving the conductivity of the positive electrode active material, and includes, without limitation, graphite such as natural graphite and artificial graphite; carbon black, acetylene black, Ketjen black, channel black, furnace black, and the like. Carbon black such as black, lamp black and summer black; conductive fiber such as carbon fiber and metal fiber; metal powder such as carbon fluoride, aluminum and nickel powder; conductive whisker such as zinc oxide and potassium titanate; titanium oxide For example, a conductive metal oxide such as a conductive metal oxide; and a conductive material such as a polyphenylene derivative may be used.

  The binder has a function of maintaining the positive electrode active material in the positive electrode current collector and organically connecting the positive electrode active materials, for example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), Carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluoro rubber, these And the like.

  The positive electrode current collector is as described for the negative electrode current collector, and generally, a thin aluminum plate may be used as the positive electrode current collector.

  The positive electrode composition may be coated on the positive electrode current collector using a conventional method known in the art, such as a dipping method, a spray method, and a roll coating method. Various methods such as a coat method, a gravure printing method, a bar coat method, a die coating method, a comma coating method, or a mixed method thereof can be used.

  The positive electrode and the positive electrode composition that have undergone such a coating process undergo evaporation of a solvent or a dispersion medium, denseness of the coating film, and adhesion between the coating film and the current collector during the subsequent drying process. At this time, drying is performed by a usual method, and this is not particularly limited.

  The separation membrane is not particularly limited in its material, physically separates the positive electrode and the negative electrode, has an electrolyte and ion permeability, and is usually used as a separation membrane in an electrochemical device. Although it can be used without any particular limitation, it is a porous, non-conductive or insulating material, especially one that has a low resistance to ion migration of the electrolyte, but has excellent moisture-absorbing ability of the electrolyte. Is preferred. For example, a polyolefin-based porous membrane (membrane) or a nonwoven fabric can be used, but is not limited thereto.

  Examples of the polyolefin-based porous membrane, high-density polyethylene, linear low-density polyethylene, low-density polyethylene, polyethylene such as ultra-high-molecular-weight polyethylene, polypropylene, polybutylene, a polyolefin-based polymer such as polypentene alone, or A film formed of a polymer in which these are mixed is exemplified.

  Examples of the nonwoven fabric include, in addition to the above-mentioned polyolefin-based nonwoven fabric, polyphenylene oxide (polyphenylene oxide), polyimide (polyimide), polyamide (polyamide), polycarbonate (polycarbonate), polyethylene terephthalate (polyethylene phthalate), and polyethylene naphthalate (polyethylene phthalate). Polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyethersulfone, polyetherether A nonwoven fabric formed of a polymer such as polyetheretherketone, polyester alone, or a mixture thereof may be used. Such a nonwoven fabric may be a fiber that forms a porous web, and may be a fiber. Including spunbond or meltblown forms composed of fibers.

  The thickness of the separation membrane is not particularly limited, but is preferably in the range of 1 to 100 μm, and more preferably in the range of 5 to 50 μm. If the thickness of the separation film is less than 1 μm, mechanical properties cannot be maintained. If the thickness exceeds 100 μm, the separation film acts as a resistance layer and battery performance is reduced.

  Although the size and porosity of the pores of the separation membrane are not particularly limited, it is preferable that the size of the pores is 0.1 to 50 μm and the porosity is 10 to 95%. If the pore size of the separation membrane is less than 0.1 μm or the porosity is less than 10%, the separation membrane will act as a resistance layer, and the pore size will exceed 50 μm, If the porosity exceeds 95%, mechanical properties cannot be maintained.

  The electrolyte may be a non-aqueous electrolyte or a solid electrolyte that does not react with lithium metal. Preferably, the electrolyte is a non-aqueous electrolyte and includes an electrolyte salt and an organic solvent.

The electrolyte salt contained in the non-aqueous electrolyte is a lithium salt. As the lithium salt, those commonly used in electrolytes for lithium secondary batteries may be used without limitation. For example, as the anion of the lithium salt, F ⁻ , Cl ⁻ , Br ⁻ , I ⁻ , NO ₃ ⁻ , N (CN) ₂ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , (CF ₃ ) ₂ PF ₄ ⁻ , (CF ₃ ) ₃ PF ₃ ⁻ , (CF ₃ ) ₄ PF ₂ ⁻ , (CF ₃ ) ₅ PF ⁻ , (CF ₃ ) ₆ P ⁻ , CF ₃ SO ₃ ⁻ , CF ₃ CF ₂ SO _{^{3 -, (CF 3 SO 2}} ) 2 N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C - ^{_{, (CF 3 SO 2) 3}} C -, CF 3 (CF 2) 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - consists ^- and _{(CF 3 CF 2 SO 2)} 2 N Any one selected from the group, or among these It can contain more species.

  As the organic solvent contained in the non-aqueous electrolyte, those commonly used in lithium secondary battery electrolytes can be used without limitation, for example, ether, ester, amide, linear carbonate, cyclic carbonate, etc. May be used alone or in combination of two or more. Among them, a carbonate compound that is typically a cyclic carbonate, a linear carbonate, or a mixture thereof can be included.

  Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (propylene carbonate, PC), 1,2-butylene carbonate, 2,3-butylene carbonate, and 1,2-pentylene. There is any one selected from the group consisting of carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and a halide thereof, or a mixture of two or more thereof. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

  Further, specific examples of the linear carbonate compound include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate and ethyl propyl carbonate. One or a mixture of two or more of them may be typically used, but is not limited thereto.

  In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, have a high dielectric constant as a high-viscosity organic solvent, so that the lithium salt in the electrolyte can be further dissociated. If a low-viscosity, low-dielectric-constant linear carbonate such as dimethyl carbonate and diethyl carbonate is mixed with such a cyclic carbonate at an appropriate ratio, an electrolyte having higher electric conductivity can be prepared.

  In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether and ethyl propyl ether, or two of them are selected from the group consisting of ethers. The above mixture can be used, but is not limited thereto.

  And, as the ester in the organic solvent, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ -Any one selected from the group consisting of valerolactone and ε-caprolactone, or a mixture of two or more thereof may be used, but is not limited thereto.

  The injection of the non-aqueous electrolyte may be performed at an appropriate stage during the manufacturing process of the electrochemical device according to the manufacturing process and required physical properties of the final product. That is, it may be applied before assembling the electrochemical device or at the final stage of assembling the electrochemical device.

  The lithium secondary battery according to the present invention can perform a lamination, stacking and folding process of a separator and an electrode, in addition to a general process of winding. The battery case may have a cylindrical shape, a square shape, a pouch type, a coin type, or the like.

  As described above, the lithium secondary battery including the negative electrode according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention, so that portable devices such as mobile phones, notebook computers, digital cameras, and hybrid devices can be used. It is useful in the field of electric vehicles such as an electric vehicle (hybrid electric vehicle, HEV).

  Hereinafter, in order to facilitate understanding of the present invention, preferred examples and experimental examples will be described. However, the following examples and experimental examples are merely to help understanding of the present invention, and the present invention is not limited to the following examples and experimental examples.

Example 1 Manufacture of a lithium secondary battery including a negative electrode coated with a multi-layered protective layer A first protective layer containing 20% by weight of HFP containing PVdF-HFP and a LiPON were formed on a negative electrode of a lithium metal plate having a thickness of 20 μm. A second protective layer and a third protective layer containing 5% by weight of PVdF-HFP were formed.

  The first protective layer was prepared by adding 20% by weight of PVdF-HFP to a solvent NMP to prepare a 20% by weight solution, coating the lithium metal plate with a slot die, and then drying at 120 ° C. for 30 minutes. It was formed with a thickness of 2 μm.

  The second protective layer was formed to a thickness of 1 μm on the first protective layer by reactive sputtering of a solution containing LiPON.

  The third protective layer was prepared by adding 5% by weight of PVDF-HFP to a solvent NMP to prepare a 10% by weight solution, coating the second protective layer with a slot die, and then drying at 120 ° C. for 30 minutes. To a thickness of 2 μm.

In addition, a positive electrode was manufactured using LCO (LiCoO ₂ ) as a positive electrode active material. Using N-methylpyrrolidone (NMP) as a solvent, a slurry was prepared by mixing LCO: Super-P: PVDF = 95: 2.5: 2.5 by weight to produce a slurry having a thickness of 12 μm. A 70 μm thick positive electrode was manufactured by coating on a foil.

After interposing polyethylene having a thickness of 20 μm as a separation membrane between the positive electrode and the negative electrode, a solvent of ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) An electrolyte containing 1.0 M of LiPF ₆ as a lithium salt and 2% by weight of vinylene carbonate (VC) as an additive was injected into the mixture to manufacture a lithium secondary battery.

Example 2 Production of a lithium secondary battery including a negative electrode coated with a multilayer protective layer A first protective layer including polyurethane, a second protective layer including LiPON, and HFP 5 on a negative electrode of a lithium metal plate having a thickness of 20 μm. A third protective layer containing PVdF-HFP by weight was formed.

  The first protective layer was prepared by adding a polyurethane (Shore hardness: 80A) to a solvent NMP to prepare a 20 wt% solution, coating the lithium metal plate with a slot die, and drying it at 120 ° C. for 30 minutes to obtain a thickness. It was formed at 2 μm.

  The second protective layer was formed to a thickness of 1 μm on the first protective layer by reactive sputtering of a solution containing LiPON.

  The third protective layer was prepared by adding 5% by weight of PVDF-HFP to a solvent NMP to prepare a 10% by weight solution, coating the second protective layer with a slot die, and then drying at 120 ° C. for 30 minutes. To a thickness of 2 μm.

In addition, a positive electrode was manufactured using LCO (LiCoO ₂ ) as a positive electrode active material. Using N-methylpyrrolidone (NMP) as a solvent, a slurry was prepared by mixing LCO: Super-P: PVDF = 95: 2.5: 2.5 by weight to produce a slurry having a thickness of 12 μm. A 70 μm thick positive electrode was manufactured by coating on a foil.

After interposing polyethylene having a thickness of 20 μm as a separation membrane between the positive electrode and the negative electrode, a solvent of ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) An electrolyte containing 1.0 M of LiPF ₆ as a lithium salt and 2% by weight of vinylene carbonate (VC) as an additive was injected into the mixture to manufacture a lithium secondary battery.

Example 3 Manufacture of a lithium secondary battery including a negative electrode coated with a multi-layered protective layer A first protective layer including 20% by weight of HFP and a LiBON including 20% by weight of HFP on a negative electrode of a lithium metal plate having a thickness of 20 μm. A second protective layer and a third protective layer containing 5% by weight of PVdF-HFP were formed.

  The first protective layer was prepared by adding 20% by weight of PVdF-HFP to a solvent NMP to prepare a 20% by weight solution, coating the lithium metal plate with a slot die, and then drying at 120 ° C. for 30 minutes. It was formed with a thickness of 2 μm.

  The second protective layer was formed to a thickness of 1 μm on the first protective layer by reactive spotting a solution containing LiBON.

  The third protective layer was prepared by adding 5% by weight of PVDF-HFP to a solvent NMP to prepare a 10% by weight solution, coating the second protective layer with a slot die, and then drying at 120 ° C. for 30 minutes. To a thickness of 2 μm.

In addition, a positive electrode was manufactured using LCO (LiCoO ₂ ) as a positive electrode active material. Using N-methylpyrrolidone (NMP) as a solvent, a slurry was prepared by mixing LCO: Super-P: PVDF = 95: 2.5: 2.5 by weight to produce a slurry having a thickness of 12 μm. A 70 μm thick positive electrode was manufactured by coating on a foil.

After interposing polyethylene having a thickness of 20 μm as a separation membrane between the positive electrode and the negative electrode, a solvent of ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) An electrolyte containing 1.0 M of LiPF ₆ as a lithium salt and 2% by weight of vinylene carbonate (VC) as an additive was injected into the mixture to manufacture a lithium secondary battery.

Example 4 Manufacture of a lithium secondary battery including a negative electrode coated with a multi-layer protective layer A first protective layer containing 20 wt% of HFP and 20% by weight of PVdF-HFP on a negative electrode of a lithium metal plate having a thickness of 20 μm, including LiPON A second protective layer and a third protective layer containing polyurethane were formed.

  The first protective layer was prepared by adding 20% by weight of PVdF-HFP to a solvent NMP to prepare a 20% by weight solution, coating the lithium metal plate with a slot die, and then drying at 120 ° C. for 30 minutes. It was formed with a thickness of 2 μm.

  The second protective layer was formed to a thickness of 1 μm on the first protective layer by reactive sputtering of a solution containing LiPON.

  The third protective layer was prepared by adding a polyurethane (Shore hardness 75D) to a solvent NMP to prepare a 20% by weight solution, coating the second protective layer with a slot die, and then drying at 120 ° C. for 30 minutes to form a thick layer. It was formed with a thickness of 2 μm.

In addition, a positive electrode was manufactured using LCO (LiCoO ₂ ) as a positive electrode active material. Using N-methylpyrrolidone (NMP) as a solvent, a slurry was prepared by mixing LCO: Super-P: PVDF = 95: 2.5: 2.5 by weight to produce a slurry having a thickness of 12 μm. A 70 μm thick positive electrode was manufactured by coating on a foil.

After interposing polyethylene having a thickness of 20 μm as a separation membrane between the positive electrode and the negative electrode, a solvent of ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) An electrolyte containing 1.0 M of LiPF ₆ as a lithium salt and 2% by weight of vinylene carbonate (VC) as an additive was injected into the mixture to manufacture a lithium secondary battery.

<Comparative Example 1> Production of a lithium secondary battery without a multilayer protective layer Example 1 was repeated except that the first protective layer, the second protective layer, and the third protective layer were not produced and coated in Example 1. It was manufactured in the same manner as in the above process.

<Comparative Example 2> Preparation of a lithium secondary battery without the first protective layer A lithium secondary battery was prepared in the same manner as in Example 1, except that the first protective layer was not formed and was not coated.

<Comparative Example 3> Preparation of a lithium secondary battery without the second protective layer The same procedure as in Example 1 was performed except that the second protective layer was not formed and coated in Example 1.

<Comparative Example 4> Preparation of a lithium secondary battery without the third protective layer A lithium secondary battery was prepared in the same manner as in Example 1 except that the third protective layer was not formed and was not coated.

<Experimental example> Battery performance evaluation The performance of each of the batteries manufactured in Examples 1 to 4 and Comparative Example was evaluated. At this time, charging and discharging conditions are as follows.
Charging: 0.2C rate control, 4.25V voltage, CC / CV (5% current cut at 1C)
Discharge: rate-limiting 0.5C, voltage 3V, CC

  While repeating the cycle under the above conditions, the number of cycles when the discharge capacity reached 80% compared to the initial capacity of the battery was measured, and the results are shown in Table 1 below.

  As shown in Table 1, in Examples 1 to 4 in which all the first to third protective layers were applied, the growth of lithium dendrite was suppressed, and the number of cycles to reach a discharge capacity of 80% was smaller than that in Comparative Examples 1 to 4. It was found that the number increased significantly.

  In the case of Comparative Example 2 in which the first protective layer was not formed, the cell performance was not improved due to poor interface formation, and in the case of Comparative Example 3 in which the second protective layer was not formed, the ability to suppress dendrite growth with insufficient strength was obtained. fell. In the case of Comparative Example 4 in which the third protective layer was not formed, the pressure due to the volume change due to the suppression of the growth of dendrites in the second protective layer could not be alleviated, so that the second protective layer was destroyed during the cycle and the performance of the battery deteriorated. Was. In the case of Comparative Example 1, since the protective layer of the present invention was not formed, the number of cycles reaching 80% of the discharge capacity was the smallest. That is, the battery of Example 1 of the present invention exhibited the most excellent battery performance.

Reference Signs List 100 Negative electrode for lithium secondary battery 110 Lithium metal layer 120 First protective layer 130 Second protective layer 140 Third protective layer

Claims (5)

Lithium metal layer;
A first protective layer formed on the lithium metal layer and maintaining an interface with the lithium metal layer;
A second protective layer formed on the first protective layer and physically suppressing dendrite growth; and a third protective layer formed on the second protective layer and supporting a structure of the second protective layer; only including,
The first protective layer has an ion conductivity of 10 ⁻⁷ S / Cm or more and an electrolyte absorbency of 150% by weight or more,
The first protective layer includes at least one selected from the group consisting of a PVdF-HFP polymer, a polyurethane polymer, and a polyacryl polymer.
The second protective layer has a Young's modulus of 5 GPa or more, a Li ion conductivity of 10 ^-7 S / Cm or more, and an electrolyte absorption of 150 wt% or less,
The second protective layer, LiPON, LiBON, zirconium oxide, beta-alumina, LISICON _{compounds, Li 2 S-P 2 S} 5 based _{compounds, Li 3 N, LiI, Li} 5 NI 2, Li 3 N-LiI- _{LiOH, LiSiO 4, LiSiO 4 -LiI} -LiOH, Li 2 SiS 3, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, Li 2 S, Li 2 S-SiS 2, Li 2 S-GeS 2, Li _{2 S-B 2 S 5,} Li 2 S-Al 2 S 2, Li 2 O-Al 2 O 3 -TiO 2 -P 2 O 5, CaF 2, AgI, RbAg 4 I 5, PVdF-HFP polymer, Polyurethane-based polymer, including one or more selected from the group consisting of polypropylene-based polymer and polycarbonate-based polymer,
The third protective layer has an ionic conductivity of 10 ⁻⁵ S / Cm or more and an electrolyte absorbency of 150% by weight or less,
The negative electrode of claim 2, wherein the third protective layer includes at least one selected from the group consisting of a PVdF-HFP polymer, a polyurethane polymer, and a polyacryl polymer . A lithium secondary battery comprising the negative electrode according to claim 1 .   The negative electrode of claim 1, wherein the first protective layer comprises a PVdF-HFP polymer having an HFP content of 15 wt% or more.   The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the second protective layer is 1 m to 10 m.   The negative electrode of claim 1, wherein the third protective layer comprises a PVdF-HFP polymer having an HFP content of 5 to 15 wt%.

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